The present invention relates in general to electrical power distribution in structures.
The inventor's previous U.S. Pat. No. 4,011,482 discloses a circuit suitable for controlling lighting in a building from multiple points. An alternating current to a light bulb or other electrical load is controlled by a triac, which in turn is controlled by the output of a series of exclusive OR gates (Ex-OR gates). The output of each Ex-OR gate is connected to the input of an adjacent Ex-OR gate except that the output of the last Ex-OR gate of the series is connected to control the input to the triac. Switches connecting to the remaining inputs of each of the Ex-OR gates can independently determine energization or de-energization of the light bulbs or other electrical load.
Although the inventor's previous invention allowed for some improved efficiency of installation, there were several practical limitations. A first limitation was that the triac alone design disadvantageously required a heat sink because of power dissipated in the triac. In addition, the problem of power dissipation and potential thermal breakdown was compounded by environmental factors including limited air circulation when installed in a ceiling or wall. This was particularly problematic in a lighting control application since power dissipated by the load would tend to create additional heating. In addition, the inventor's previous invention did not disclose load fuse protection at the control unit. Nor did the inventor's previous invention provide thermal fuse protection of the control circuitry to improve safety.
The limitations of the inventor's previous invention indicate a need for an improved thermal design, and an improvement in energy efficiency. This includes limiting heat dissipation which is additionally important in the thermally challenging environments of in-wall and in-ceiling installations, particularly when containing thermal insulation.